ISO 12v BMS that can handle series 36v, high burst and iPhone bluetooth app

[Fish Freak]

My question will help many others, I'm sure, that are in the same boat;

Will's vids convinced me it'll be super simple to build my own LifePO4 power storage, not for solar, but for my fishing boat. I like the idea of DIY, learning, and using top quality parts compared to the 'cheap' drop-in lead-acid replacements. Found some great prismatic cells he tested, but then when I got to BMS I keep finding that they 'cannot be used in series' and no iPhone (android only) monitor app. I'm on the verge of giving up because I don't believe the Alibaba, ebay listings that say 'low temp protection' when Will proves that most don't work.

Who makes a battleborn grade BMS that also has a bluetooth app for iOS, not just android? A configurable app, not just to 'view' the SOC, Ah, etc.?

I run 4 group 27 to 31 big heavy lead agm batteries; 3 in series for 36v (or 2s for 24v) trolling motor (57 amp max draw) and one single 31 agm for starting a large boat engine (need burst, about 300 amps) and powering many electronic devices onboard all day. Going to LifePO4 represents a HUGE weight savings, and performance benefit. So what I'd like to understand is, why can't most BMS' be used in series? Why does a 12v BMS even care that it's in series? I could see if you were drawing AND charging in 36v like you would with solar, however, in our boats we use a 4 bank waterproof lithium charger that pushes say 20 amps to 4 leads, so each of the 4 batteries are recharged individually in 12v. Does charging individually in 12v negate that 'no series' warning?

My last goal would be to have one of my 4 DIY LifePO4 batteries be able to start an IC gas engine, needs roughly 300 amps for a quick burst, but then needs to power all sorts of electronics all day. So the BMS needs to be tough, right? Does one exist yet for a fair under $100 price? How about over $100?

Part of what's bugging me is there is a CHEAP $$ line of drop-in lead acid replacement batteries called Ionic, that can be used in series, can do the burst amps for starting an IC, and they have bluetooth, and I'm wondering HOW they're doing all that so cheap? I'd love to see Will cut one of them open!!

BTW I found some cool waterproof cases I think would be slick for battery cases with SEE_THRU tops, by Bud Industries, many sizes in their NEMA PTQ series:

 

[Fish Freak]

Anyone?

 

[tictag]

So what I'd like to understand is, why can't most BMS' be used in series? Why does a 12v BMS even care that it's in series?

Not 100% sure but it might be because of the higher voltages (wrt to ground) involved in series-connecting batteries or that the BMS will not have a ground reference i.e. the 'ground' of one will be at the the potential of the sum of all behind it. But I genuinely don't know. The current won't change i.e. if the battery is rated for 100A, only 100A will every flow through the battery. Maybe if one battery BMS were to disconnect a specific battery, would that cause problems with the others in the string? Somebody cleverererer than me on BMS matters will likely pipe up.

Please also note that you do not strictly-speaking need a BMS that cuts the supply line. There are plenty that just offer balancing and data.

And going even further, strictly speaking you do not need a BMS! Though I would not recommend this.

Does charging individually in 12v negate that 'no series' warning?

Yes. When batteries are connected in parallel, each 'leg' contributes to overall current flow, meaning that the BMS would only need to support the current from one battery.

So the BMS needs to be tough, right? Does one exist yet for a fair under $100 price? How about over $100?

Most BMS will have a surge-current specification, you need to check the specs for this. Typically, this is 2x operating current for <1 second.

I am not up on BMS prices, sorry.

BTW I found some cool waterproof cases I think would be slick for battery cases

Nowt wrong with keeping your Lithium-ion batteries in a battery box, but you don't really need to. Different chemistry, different technology to lead-acid.

Good luck with your new system!


Edit: Corrected utter bull-crap about current increasing through series-connected batteries. Thanks @Fish Freak !!

 

[Fish Freak]

Most, but certainly not all, BMS' switch the battery on/off using active devices such as FETs, depending on various protection scenarios (e.g. cell over-voltage), which means that the entire load current has to flow through the BMS. 100A, a typical BMS current limit, is a lot of current to be flowing through a silicon-based device. Put two in series and you now have 200A flowing through a silicon-based device, three is 300A etc. An alternative is to use a contactor for switching the supply line, like the Chargery-branded BMS'. These are less efficient because the contactor coil is permanently energised i.e. draws a permanent supply in order to function.

Please also note that you do not strictly-speaking need a BMS that cuts the supply line. There are plenty that just offer balancing and data.

And going even further, strictly speaking you do not need a BMS! Though I would not recommend this.

Yes. When batteries are connected in parallel, each 'leg' contributes to overall current flow, meaning that the BMS would only need to support the current from one battery.

Most BMS will have a surge-current specification, you need to check the specs for this. Typically, this is 2x operating current for <1 second.

I am not up on BMS prices, sorry.

Nowt wrong with keeping your Lithium-ion batteries in a battery box, but you don't really need to. Different chemistry, different technology to lead-acid.

Good luck with your new system!

Oh so you're saying that when my 12v battery bms is tied in series to another it has to be able to handle double the amps? The series restrictions have nothing to do with charging in 24v or 36v?

What puzzles me is there are relatively inexpensive lithium batteries out there that I know people are putting in series in my same application with no problems. My application is modular, my motor can run in 24v or 36v depending on how much power I need. My charging system is 12v multi-bank waterproof charger too. The amp draw is fairly low too, 57 amps max at 100% and I'm rarely that high for very long at all. Nominal use is easily half that. My circuit breaker is 60 amp so I'll never get to 100. I'd think, or hope, if I get a 120 amp BMS like this one Will tested, I'd be okay?

DYKB Smart BMS 120 Amp with bluetooth

I'm trying to DIY a battery with the quality of Battleborn but the features of this one: Ionic Bluetooth Lithium. Their specs say they can run up to 4 in series. I want to put them in a waterproof container because they could get splashed occasionally in my boat. The cells could be exposed but then I'd need the BMS to be enclosed.

I really appreciate your feedback Tictag, I really thought this would be easier...

 

[tictag]

Oh so you're saying that when my 12v battery bms is tied in series to another it has to be able to handle double the amps?

Actually, no! Clearly I was on some mushrooms or something when I wrote that post!! I'll re-read it and correct. Sorry for the confusion - confused me and I wrote it!!

 

[tictag]

My last goal would be to have one of my 4 DIY LifePO4 batteries be able to start an IC gas engine, needs roughly 300 amps for a quick burst, but then needs to power all sorts of electronics all day.

BMS's usually come in three flavours:

1. Those that come with internal battery disconnects
2. Those that control external battery disconnects
3. Those that do not offer such protection, simply balance and surface data via, for example, Bluetooth

I would never recommend running Lithium-ion without a BMS but option (2) above might work. Contactors can be bought rated for hundreds, if not thousands of amps - check out the Chargery BMS range. And just for info, Lithium-ion batteries can be discharged at waaaaaaaaaaay higher rates than lead-acid. 300A? A 15AH pocket-sized 18650 pack would spit that out without even noticing it had done so.

My circuit breaker is 60 amp so I'll never get to 100. I'd think, or hope, if I get a 120 amp BMS like this one Will tested, I'd be okay?

I personally wouldn't buy such a cheap BMS, especially as this one has a mobile phone module in it, which I wouldn't have use for. Imho, BMS's are there to protect your investment, and that investment is considerable. How much are the cells costing you? I think spending maybe 10% of the cell cost to protect them doesn't seem unreasonable.

Anyway, I'm actually struggling to figure out exactly what you are trying to do. Do you need to simply replace your existing lead-acid capacity with Lithium-ion? Most people wouldn't do this. They would first work out how much energy they need, then spec a battery that fulfils that need.

 

[Fish Freak]

BMS's usually come in three flavours:

1. Those that come with internal battery disconnects
2. Those that control external battery disconnects
3. Those that do not offer such protection, simply balance and surface data via, for example, Bluetooth

I would never recommend running Lithium-ion without a BMS but option (2) above might work. Contactors can be bought rated for hundreds, if not thousands of amps - check out the Chargery BMS range. And just for info, Lithium-ion batteries can be discharged at waaaaaaaaaaay higher rates than lead-acid. 300A? A 15AH pocket-sized 18650 pack would spit that out without even noticing it had done so.

I personally wouldn't buy such a cheap BMS, especially as this one has a mobile phone module in it, which I wouldn't have use for. Imho, BMS's are there to protect your investment, and that investment is considerable. How much are the cells costing you? I think spending maybe 10% of the cell cost to protect them doesn't seem unreasonable.

Anyway, I'm actually struggling to figure out exactly what you are trying to do. Do you need to simply replace your existing lead-acid capacity with Lithium-ion? Most people wouldn't do this. They would first work out how much energy they need, then spec a battery that fulfils that need.

Yes I've already done the math; I'm replacing 3 large heavy (70 lb x 3 = 210 lbs) 12v deep cycle lead acid batteries with 3 light-weight (approx 25 lbs x 3 = 75 lbs) LiFePO4 12v cells and remove 135 lbs from my boat. That's not all, because those 3 are only a start. The boat has a separate house battery that powers navigation electronics and such plus starts the outboard engine, and there's another 45 lbs for a total of 180 lbs of weight savings. I'll be removing on board charging systems to save even more. Weight savings are my motivation and a giant performance improvement in this application.

These LifePO4 specs actually have way more capacity than my lead ballasts, since lead acid can only be drawn down 50%, but I plan to cycle the LiFePO4 cells from 40% to 75% capacity to ensure long life and to never hit min/max temp or volts.

My plan is to get these crazy cheap 3.2v LiFePO4 120Ah cells from Shenzhen Xuba Electronic Trading Co. on Alibaba, if I'm seeing this correctly they're only $37 usd a piece?!? If I bought a single 3.2v 100Ah cell like that from Fortune it'd be $150.

I do see that the BMS is the heart of my battery system, and I'd really like to get the best available, but I have no clue what that is? I've just begun this lithium journey, and thanks to Will's videos, I'm diving in. My thought process is, maybe I'll start with making two 12v cells with this cheap BMS that has an iPhone app and will let me set charge and discharge levels and see how that works? It seems like this is the ONLY bms with support for Apple devices, so that's why I've gone this way. I do not think external relays are necessary because I do not see others using them, they're just using Battleborn and Ionic drop-in style batteries. I'm guessing though, because I've heard that because lithium tech batteries draw charge at such higher levels, they can tax a gas engine's alternator and fry it. Hoping that won't happen but it's a risk at this point I'm not sure how to deal with. Hoping that I can limit charge voltage or current with the BMS app and thereby take the load off the alternator.

If there's a high quality BMS that you know can do this, please chime in.

What will happen if I try to start an engine that requires about 300 amps for just a few seconds, with this cheap 120A BMS?

What will happen if I take two of these 12v batteries with this cheap BMS and put them in series for 24v, and draw less than 60 amps, more like 30 or 40 most of the time? Gauging from the 100 amp BMS that was in the Battleborn that Will cut open, I think this all may work?!?! Lol, hope I don't fry everything!

 

[tictag]

Just a couple of clarifications first.

You have two battery banks, Bank A and Bank B, what is Bank A used for? You say that Bank B powers your electronic devices but also starts your outboard - is this the best configuration? I mean even lithium-ion will drop voltage supplying huge loads like a starter motor, and this puts your electronic devices at greater risk of brown-out.

Another clarification, you say, "I do see that the BMS is the heart of my battery system", I think you maybe misinterpreting what a BMS does. You later say, "Hoping that I can limit charge voltage or current with the BMS app and thereby take the load off the alternator.". A BMS does not in any way affect charging rates, in fact it doesn't control anything at all. The principle purpose of a BMS is to protect the battery and it does this in two principle ways:

1. Keeps the cells balanced
2. Disconnects the battery under certain conditions

Those conditions are, for example, short-circuit, over-voltage, over-discharge etc. It does not control such things and in a very real sense you can just ignore it as far as the rest of your system is concerned - your system needs to be designed to work within the thresholds your BMS sets - otherwise it will disconnect your battery. It's like a bouncer at a club, chucking you out if you misbehave.

You say that you have, "Yes I've already done the math; " but then go onto simply specifying your existing battery capacity, I infer from this that you simply intend to replace your existing battery capacity with lighter lithium-ion capacity. This is not what I meant about doing an 'energy audit'. An energy audit will help you determine what the 'right' battery capacity is i.e. to support your energy consumption. It might well turn out that you don't need as much capacity as you have now, further reducing the weight taken up by batteries.

But, just thinking about this a bit more, on a boat do always run the engine/alternator to power your loads? Or do you rest-up and expect your battery to power the loads?

For the former scenario, I guess you just need a battery capable of starting the engine(s) then the alternator would presumably power everything, including a charger to replenish the battery. In the latter scenario you will need a sufficient battery capacity to power your loads for however long you plan to rest-up. These are two very different usage scenarios that may well require two different approaches when it comes to BMS selection.

To answer your question, "What will happen if I try to start an engine that requires about 300 amps for just a few seconds, with this cheap 120A BMS? ", it will just instantly disconnect your battery (best case). As far as the BMS is concerned, that might as well just be a short-circuit.

Now you could just go with a BMS that only offers cell balancing and data i.e. no battery disconnect, but I would not recommend this. So a BMS that has external contactors to disconnect the load is probably best. The BMS and its contactor would have to support super high loads, for example, the Chargery BMS16T can support loads of up to 600A.

I'm going to assume that your Bank A is just there to start your main engine. How much current is required to do this? LiFePO4 batteries can be safely discharged at up to around 1C, meaning that a 100AH battery can safely discharge at up to 100A. So to discharge at 1,000A, for example, you would need 10 x 100AH batteries connected in parallel. LiPo batteries can be safely discharged at much higher rates e.g. 20C, 30C etc. But this battery chemistry is, relative to LiFePO4, much more dangerous and is incredibly volatile if the active material were to ever come in contact with water. Not something I would recommend for a boat!!

You can get LiFePO4 batteries rated for higher discharge rates, but I am not so familiar with these; could be a good option for your starter bank.

I would recommend having a separate battery for your outboard. You don't want it connected to your house battery because of the increased risk of brown-outs and you don't want it connected to your starter battery because if it goes flat for any reason, you'll be stranded with no means of propulsion.

For your house battery, now you are in the realm of energy audits and determining how long you would like to power your devices without the alternator running. For example:

Device	Rating (W)	Time (h)	Energy (Wh)
Kettle	1,200W	0.5	600Wh
Lighting	50W	6h	300Wh
TV	40W	4h	160Wh
"	"	"	"
		TOTAL	1,060Wh

So in the above example, you'd need a 1,060Wh battery to supply your energy consumption for 24 hours. Want to lay up for two days? Double it. Three days? You get the picture.

Note: to convert Wh to AH you simply divide the Wh by the voltage e.g. 1,060Wh at 12V = 88AH.

When charging a Lithium-ion battery from an alternator source you have to be very careful to avoid drawing too much current from the alternator. Lithium-ion chemistry batteries have a very low internal resistance so will draw hundreds of Amps if it can. Alternators tend to be cooled by fins on the alternator itself so low revs e.g. idle, represents minimum possible cooling. One solution is to fit a smart alternator that has in-built current limiting or, what most people do is use a DC-DC charger instead of relying on the alternator's own charging circuit. An example of such a device would the Victron Orion chargers. Other manufacturers are available!

What will happen if I take two of these 12v batteries with this cheap BMS and put them in series for 24v, and draw less than 60 amps, more like 30 or 40 most of the time? Gauging from the 100 amp BMS that was in the Battleborn that Will cut open, I think this all may work?!?! Lol, hope I don't fry everything!

Yes, connecting two such batteries in series would provide a 24V(nominal) battery, which would halve the current to a given load .... but, and here's the kicker, your devices need to be designed specifically for a 24V supply, which I'm guessing most of your are not.

Lot's to think about here but the next steps are:

1. Confirm what Bank A does. Starter bank?
2. Confirm how many Amps are needed to start the main engine.
3. Research high discharge rate LiFePO4 batteries.
4. Research and get your head around the three flavours of BMS's i.e. (1) Balance only, plus data, (2) Balance, data & internal disconnect e.g. Daly, (3) Balance, data & external disconnect e.g. Chargery.
5. Research Smart Alternators versus DC-DC chargers.

Ultimately we'll want to determine what is the best battery technology and capacity for your starter bank, what capacity is the best capacity for your house bank, and how best to charge them both.

My gut instinct is that simply replacing your existing lead-acid capacity with Lithium-ion would be serious over-kill and would cost you far more than needs be. I also believe that the weight savings you are expecting can be improved upon

 

[tictag]

p.s. that post has broken my personal best in terms of post length!! Could have written a book with fewer words

 

[craz z]

Build your packs to suit the needs of each individual charger. buy the bms that coordinates with each system.
Grab this one for 12v low temp disconect (4s) get the bluetooth acc.
get an ANT or Daly for 24v (8-12s)

Both come in bluetooth except for daly.

Run the starter on a lead acid if possible. high current spikes or c ratings on a bms controlled battery is likely to trip. not healthy on the battery any way

Series is the name of the game with low voltage cells but bms's limit voltage on the entire pack as a whole. DIY lifepo4 bms range on how many series connections. store bought packs may have some auto voltage up to a certain number whether it be 48v or below. allowing them to series connect.

DIY packs with the bms's available run in series of cells based on how many (S's) you wanna go .

Look for a battery isolation solution for the alternator or send all charging to the starter battery. onboard charging when you come off the water. or small solar panel if you have space

boats have weird onboard charging configurations. battery outputs can be 24-36v but the way the chargers are setup on multibank onboard chargers is still utlizing 12v outputs to the batteries even in a 24-36v series configuration. often times they will branch off one of the batteries in series to "stepdown" back to 12v for fishfinders etc. its weird but works to cut costs out as 24v chargers are not very common. its a work around

my guess is in 36v mode is the same as the 24v as far as output but adding more runtime cause of voltage sag. 24vs36

tictag outlined it really well. for safety you want the boat to start no matter what so starting system must be separate from the system. with an option to boost charge if you get in a pickle. you can add a relay to one of your lifepo4 12v packs on a momentary switch for aux starting power.

 

[Fish Freak]

p.s. that post has broken my personal best in terms of post length!! Could have written a book with fewer words

Hey, don't think your words went unnoticed! Read them all and thank you for all that consideration! I have done the audit to the extent that I need to, for my boat is small and I won't be doing any overnight trips in it. It does however have some sophisticated electronics, and it's very fast, so weight is a huge motivation for doing this. Everything is a compromise, and for me it's space and weight. That also means no isolated house battery for electronics and separate starting battery. It's not a big deal because I'll have one of the 24v on a breaker so I can use it to 'jump' the house battery for a second if I need to.

I understand what you're saying about lifepo4 cell and how it can 'pull' hundreds of amps from the alternator and 'smoke it' - that is one of my big concerns, and because of that I'm considering a bms that has a separate charge and load port, and I'll try programming via bluetooth app it to a lower voltage when I'm on the fly, then say when I'm charging so that it doesn't tax the alternator too much. I know, it sounds risky, but there are a bunch of guys with my class boats that are doing it, but they're buying Battleborn, or Ionic batteries off the shelf. Fortunately my alternator is a low-amp version, however I'm still looking for some kind of a regulator other than connecting a lead-acid battery and a DC/DC charger.

 

[Fish Freak]

Build your packs to suit the needs of each individual charger. buy the bms that coordinates with each system.
Grab this one for 12v low temp disconect (4s) get the bluetooth acc.
get an ANT or Daly for 24v (8-12s)

Both come in bluetooth except for daly.

Run the starter on a lead acid if possible. high current spikes or c ratings on a bms controlled battery is likely to trip. not healthy on the battery any way

Series is the name of the game with low voltage cells but bms's limit voltage on the entire pack as a whole. DIY lifepo4 bms range on how many series connections. store bought packs may have some auto voltage up to a certain number whether it be 48v or below. allowing them to series connect.

tictag outlined it really well. for safety you want the boat to start no matter what so starting system must be separate from the system. with an option to boost charge if you get in a pickle. you can add a relay to one of your lifepo4 12v packs on a momentary switch for aux starting power.

Hey Cray,

That Overkill Solar BMS looks pretty good. Have you tried it? Do you know if it allows series connection to other batteries? I've posed that question to the seller, awaiting reply... How about bluetooth app for iPhone? I think they said it cost a few bucks from the App store, if so, no biggie. You got that right on jumping to my other 12v packs if need be, that's what I've been doing, and that's a big reason I've got two 12v packs to make 24v series rather than building one large 24v pack. That and onboard chargins systems that already are 12v, saves cost. Thanks for your feedback.

 

[Craig]

Hey Cray,

That Overkill Solar BMS looks pretty good. Have you tried it? Do you know if it allows series connection to other batteries? I've posed that question to the seller, awaiting reply... How about bluetooth app for iPhone? I think they said it cost a few bucks from the App store, if so, no biggie. You got that right on jumping to my other 12v packs if need be, that's what I've been doing, and that's a big reason I've got two 12v packs to make 24v series rather than building one large 24v pack. That and onboard chargins systems that already are 12v, saves cost. Thanks for your feedback.

If you have 12v on board charging how do you plan to charge 24V system?

 

[Fish Freak]

If you have 12v on board charging how do you plan to charge 24V system?

Craz z had it all almost spot-on, about marine setups, because they're based on charging 12v lead acid batteries, what they have is onboard a/c chargers with 3 or 4 discrete 12v 15 or 20 amp outputs to individually charge 3-4 lead batteries. So it's no big deal to output 2 or 3 series 12v cells to 24v or 36v while still charging them at 12v.

 

[Craig]

Craz z had it all almost spot-on, about marine setups, because they're based on charging 12v lead acid batteries, what they have is onboard a/c chargers with 3 or 4 discrete 12v 15 or 20 amp outputs to individually charge 3-4 lead batteries. So it's no big deal to output 2 or 3 series 12v cells to 24v or 36v while still charging them at 12v.

Very Interesting I will have to research that. Never heard of it before. Thanks!

 

[Fish Freak]

Very Interesting I will have to research that. Never heard of it before. Thanks!

Yup it's kinda how we've been 'balancing' 36v lead series banks for decades, by individually 12v charging them. That lead is so archaic and heavy, that's why I'm learning this lithium tech.

 

[craz z]

I've been racking my brain trying to figure out how to do it. This might be an option.

Build 12v packs with battery disconnects have 2 leads one for bms one for series connection (bypass bms direct to cell post)

Use the bms only for charging top balancing you would have to disconnect the series connection when charging. You will need a low voltage disconnect preferably the smart victron with Bluetooth for discharging the cells


Fla's don't care the charger is the brain splitting the packs lithium with bms only care about what they are programmed to do 12v 24v 36v 48v if the bms sees anything outside of their program they cut the juice.

I would forget about charging with the engine an do it on the dock as you have an ac charger anyway. You'll have plenty of all day power compared to your fla's

The overkill bms is awesome from what I've read the apple app is super sweet worth the buy. I'm android and love my overkill bms. Must have enterprise paid version for programming the free version is worthless.

 

[Fish Freak]

I've been racking my brain trying to figure out how to do it. This might be an option.

Build 12v packs with battery disconnects have 2 leads one for bms one for series connection (bypass bms direct to cell post)

Use the bms only for charging top balancing you would have to disconnect the series connection when charging. You will need a low voltage disconnect preferably the smart victron with Bluetooth for discharging the cells


Fla's don't care the charger is the brain splitting the packs lithium with bms only care about what they are programmed to do 12v 24v 36v 48v if the bms sees anything outside of their program they cut the juice.

I would forget about charging with the engine an do it on the dock as you have an ac charger anyway. You'll have plenty of all day power compared to your fla's

The overkill bms is awesome from what I've read the apple app is super sweet worth the buy. I'm android and love my overkill bms. Must have enterprise paid version for programming the free version is worthless.

Actually Craz z, I'm just building 12v packs with individual BMS's and treating them like a lead agm. Is that not ok? I've not tried the Overkill bms but I intend to; I was having a conversation with a seller in CHINA, and she gave me this guy's cell number that has their stuff in the US. Lol, guess who? Steve @ Overkill. Super nice guy, we text back and forth, with all sorts of info to share, and he's got Fortune generic cells here state side ready to sell, and he already tried his BMS in series, and he said it worked fine. He agreed, the bms doesn't care if it's 12v array is connected in series to another 12v, the amp draw is the same, and easy, in my application, less than 60 amps.

So I'm building two banks, the 24v-36v array, and then a separate 12v for engine starting and accessories. Someone here showed me a high amp BMS in china here at the IC GOGOGO store, and it says it can handle 380 amps common v, or 200 amps separate v. For my cranking battery, I'm thinking that I should try that 200a that separates the charge lead and the accessories lead? Many guys have used drop-in branded lifepo4 batteries for cranking duty, but the problem is, they leave the dock with 100% charge. Engine starts great, they run 10 min across the lake, and BAM! Their navigation equip cuts off because the BMS got to overvoltage real quick from the engine's 50, 60 amp alternator, and opened the circuit. BMS did it's job correctly. Then they've got to wait until the surface charge dissipates and the BMS lets the ground get reconnected, turn on a bunch of accessories, like pumps to bring down the voltage. then proceed.

If I go with a separate ground port bms, I can put the engine start/charge on the bms' charge lead, and the accessories on the load lead. If the alternator charges up to over voltage, the charge lead disconnects, but since the accessories are on the load lead, they stay running, and only get cut off if the charge level drops too low. The engine keeps running even when there's an over voltage bms event because it doesn't need a battery to run. Is this logic correct?

Alternators do not like to be disconnected at full steam, it blows the diode. So I'll connect an alternator protection device like this one from Sterling to that charge lead ground and positive. Is this a working concept anyone??

 

[craz z]

Actually Craz z, I'm just building 12v packs with individual BMS's and treating them like a lead agm. Is that not ok? I've not tried the Overkill bms but I intend to; I was having a conversation with a seller in CHINA, and she gave me this guy's cell number that has their stuff in the US. Lol, guess who? Steve @ Overkill. Super nice guy, we text back and forth, with all sorts of info to share, and he's got Fortune generic cells here state side ready to sell, and he already tried his BMS in series, and he said it worked fine. He agreed, the bms doesn't care if it's 12v array is connected in series to another 12v, the amp draw is the same, and easy, in my application, less than 60 amps.

If Steve tested it and it works then I would go with that. I think its a cool experiment and would make a fun video for Will. We've been told by all the battery manufacturers that series connections arent allowed with their bms. I was always under the impression that if the bms's see an overvoltage condition it shuts down maybe this isn't the case based on the wiring configuration.

If I go with a separate ground port bms, I can put the engine start/charge on the bms' charge lead, and the accessories on the load lead. If the alternator charges up to over voltage, the charge lead disconnects, but since the accessories are on the load lead, they stay running, and only get cut off if the charge level drops too low. The engine keeps running even when there's an over voltage bms event because it doesn't need a battery to run. Is this logic correct?

Sounds right to me. Just make sure the accessories are fused just in case not that a FLA can't provide amps but lithium can really unload. I guess even for the start circuit technically you don't need a bms involved but you HAVE to stay in the C ratings or build a parallel bank that is large and capable of handling constant 200amp bursts for starting while staying in the advertised C ratings. Battle borns say they can handle 300amp loads for x seconds, but I'd rather not hammer a 900$ battery nor even a cheapy calb fortune cell. A start battery FLA at wally world is only a 100$ bucks

Charge circuit keep a BMS involved for certain unless its programmable solar controller which this is not.

one last thought was if any of the accessories have a potential of any kind pull a draw when not in use? then this might not work or again i'd throw a switch or disconnect to that lead.

 

[Fish Freak]

If Steve tested it and it works then I would go with that. I think its a cool experiment and would make a fun video for Will. We've been told by all the battery manufacturers that series connections arent allowed with their bms. I was always under the impression that if the bms's see an overvoltage condition it shuts down maybe this isn't the case based on the wiring configuration.

For sure Steve said it could do it, so at least I have his word. Could the bms even see that another cell was connected and the final output voltage was higher?

Sounds right to me. Just make sure the accessories are fused just in case not that a FLA can't provide amps but lithium can really unload. I guess even for the start circuit technically you don't need a bms involved but you HAVE to stay in the C ratings or build a parallel bank that is large and capable of handling constant 200amp bursts for starting while staying in the advertised C ratings. Battle borns say they can handle 300amp loads for x seconds, but I'd rather not hammer a 900$ battery nor even a cheapy calb fortune cell. A start battery FLA at wally world is only a 100$ bucks

Yes all accessories go through a fuse block on the positive terminal, so they'd never take more then they're designed for. That's good news for battle born, hitting 300 amp burst, because Will sawed that one open and it only had a 100 amp bms. If I can get that 380 amp bms and the charge leg is roughly 200, it seems like I'm better off than the BB? I'm not sure how I'll restrict load? Will most bms have the ability to release on a short high burst? I'm actully thinkin' that the cheapy prismatics coming outta China right now are at the point that I'm willing to risk trying. There are guys running cheap but big (Ionix 125) drop-in LifePO4 complete batteries with no backup FLA battery, just lithium, and they're doing fine IF they learn don't leave the dock with MORE than say about 75-80% charge? Give the alternator some room to work with.

Charge circuit keep a BMS involved for certain unless its programmable solar controller which this is not.

Always. And I intend to have headroom and stop charging at about 75%. My concern is that I'll never get a 'top balance'. Install one of these little auto-active balancers like this? How could balancing all the time be a bad thing, isn't that what these do?

one last thought was if any of the accessories have a potential of any kind pull a draw when not in use? then this might not work or again i'd throw a switch or disconnect to that lead.

I'll always have a breaker/switch on the positive accessory lead close to the battery, plus the fuse block upstream, connected with fat copper. I always disconnect that breaker because there are lots of items with little draws lurking.